In recent years, various kinds of information handling equipment are mounted on a movable body such as an automobile, allowing various kinds of information processing to be carried out. An example of information handling equipment becoming popular is a radio receiver that is capable of reproducing audio information from a broadcast wave received from a radio broadcasting station and displaying literal data such as information on traffic included in the broadcast wave. In addition, an apparatus for playing back information from a variety of audio recording media such as a compact disc (CD) is also becoming popular as the so-called car audio apparatus.
Furthermore, there are some movable bodies each having an onboard navigation apparatus for processing information included in a position measurement signal received from a source such as an artificial satellite to determine the position and the running state of the movable body.
On the top of that, there are also some movable bodies each provided with a radio telephone apparatus called a car telephone or a portable telephone allowing the movable body to establish a telephone conversation and to transmit or receive data. As such, the information handling equipment mounted on a movable body such as an automobile has been exhibiting an increasing trend in volume in recent years.
By the way, these kinds of onboard information handling equipment are installed in a vehicle with almost no relation to other information handling equipment. As an apparatus having a plurality of functions, the equipment is no more than a car audio apparatus with a radio receiver incorporated therein. Thus, each time a new piece of information handling equipment is added, it is traditionally necessary to provide wiring for installing the new equipment in the vehicle. As a result, it is necessary to provide an extremely large amount of wiring for information handling equipment installed in the automobile.
Accompanying the increasing amount of wiring, there has been developed an onboard information bus line for integrating and controlling pieces of information handling equipment by connecting the pieces of equipment to each other. Each piece of information handling equipment has a connection unit for connecting the piece of equipment to the onboard information bus line. The onboard information bus line has a configuration wherein the connection unit of each piece of information handling equipment is connected to the onboard information bus line.
However, such onboard information bus line requires electric power for operating the connection unit of each piece of information handling equipment. Thus, as the number of pieces of onboard information handling equipment increases, the required electric power may exceed the capacity of a battery which serves as a power source. For this reason, the need to save electric power further rises.
On the other hand, while it is desirable to turn off the power supply of each of information handling equipment to save electric power, the pieces of equipment can not be activated individually and independently of each other since they are connected to each other through the onboard information bus line. As a result, there arises a problem of poor operatability.